The Computer Core will provide hardware and software resources in support of the Research Projects and Cores of the Program Project. The general focus of the Computer Core is to develop and enhance computer algorithms to facilitate the research on plan optimization, dose computation, treatment implementation, uncertainty analysis and minimizatoin, and to facilitate th eimplementatoin of the research results in close coordination with the Clinical Core. Our major tasks will include the investigation and implementation of automated techniques for image correlation and segmentation, additions and enhancement to the second generation 3DRTP system focusing on the integration of the BEV, Dose Calulation, and Plan Evaluation modules, the development of a unified patient databaseintegrating various sources of information regarding treatment protocol and outcome, and the developmentand implementation of real time quality assurance for dynamic multileaf collimator treatments. The Dosimetry Core is responsible for the safe and accurate delivery of radiatoin dose and is therefore important for many aspectsof this Program Project. The radiation machines under our care for this PPG are the Varian C-Series machines (two 2100Cs and three 600Cs) and the Scanditronix MM50, all equipped with multileaf collimators. Our dose calibration protocol follows the AAPM TG21 recommendations, and patientdosimetryis based on a basic set of measured beam parameters augmented by a pencil beam convolution method forirregular field dosimetry. Of importance to this PPG is the dosimetry of MLC and its application in the dynamic mode (DMLC); the dosimetric effects of the rounded leaf-edge, output for small fields, and leaft transmission need to be considered. In addition, a comprehensive and stringest QA process for DMLC needs to be developed. For these dosimetric measurements and investigations we shall use many approaches, scanning water phantoms, films and TLD dosimetry, and Monte Carlo simulation. Finally, we shall explore the use portal imager as a means of verifying leaf motions and the intensity profiles delivered with DMLC.